BR112018006225B1 - ALLOY STEEL AND TEMPERED AND HARDENED STEEL ARTICLE - Google Patents

Abstract

an alloy steel is disclosed that provides a unique combination of strength, toughness and fatigue life. the steel alloy has the following composition, in percent by weight: from about 0.15 to about 0.30 c, from about 1.7 to about 2.3 nm, from about 0.7 to about 1.1 µm, from about 1.85 to about 2.35 µm, from about 0.5 to about 0.9 µm, from about 0.1 to about 0. 3 mo+1/2w, from about 0.3 to about 0.7 cu, from about 0.2 to about 0.5 v+5/9xnb. the alloy balance is iron, usual impurities, and residual amounts of other elements added during melting to deoxidize and/or desulfurize the alloy. a hardened and quenched steel article made from the alloy is also disclosed.

Description

Invention history Invention field

[0001] In general, this invention refers to a steel alloy that provides a unique combination of strength, toughness and fatigue duration. More particularly, the invention relates to a useful article made of steel as well as a method for making the article.

Description of the related technique

[0002] Directional drilling of oil wells often requires the use of mud engines. A mud motor (or drill motor) is a progressive cavity direct displacement pump (PCPD) placed in the drill string to provide additional power to the bit during drilling. The PCPD pump uses drilling fluid (commonly referred to as drilling mud or just mud) to create eccentric motion in the power section of the motor that is transferred as concentric energy to the drill bit via the mud motor shaft and a joint of constant speed. When the drill bit encounters deposits of varying hardness and strength during the drilling operation, transferring the eccentric motion as concentric energy across the shaft requires a strong shaft material that has high impact toughness as well as good rotational bending fatigue life . The current material of choice is the 4330V alloy which is known to provide a conventional yield strength (YS) of about 1,034 MPa (150 ksi) and a V-shaped notch impact energy for Charpy testing (CVN IE) of about 54.2 J (40 foot-pound) at room temperature.

[0003] Until recently the 4330V shaft material was acceptable. Now, with the drilling of deeper wells in different deposits, such as shale, the need has arisen for a stronger shaft material, with better tenacity than that provided by the 4330V alloy.

Invention Summary

[0004] The need described above is largely fulfilled by an alloy according to the present invention. According to one aspect of the present invention, there is provided a high strength, high impact toughness alloy steel having the following preferred broad weight percent compositions.

[0005] Included in the balance are the usual impurities found in commercial grades of alloy steels produced for similar use and small amounts of other elements retained from deoxidation and desulfurization additions during melting.

[0006] The above table is provided as a convenient summary and is not intended to restrict the lower and upper values of the ranges of the individual elements for use in combination with each other, or restrict the ranges of the elements for use only in combination with each of the others. Thus, one or more of the bands can be used with one or more of the other bands of the remaining elements. In addition, a minimum or maximum for one element of a broad or preferred composition may be used with the minimum or maximum for the same element in another preferred or intermediate composition. Here and throughout this report, the term “percent” or the symbol “%” means percent by weight or percent by mass, unless otherwise specified.

[0007] The alloy according to the present invention provides a Y.S. at room temperature of at least about 1241 MPa (180 ksi) in combination with a CVN IE of about at least about 33.9 J (25 foot-pound). The alloy is also capable of providing a CVN IE at room temperature of up to about 81.3 J (60 ft-lb) which represents a 20% increase in Y.S. and 50% in CVN IE when compared to the 4330V alloy. The alloy of this invention also provides a very good fatigue life represented by a rotational bending axial displacement stress of 620.5 MPa (90 ksi) in 10 million cycles.

[0008] According to another aspect of the present invention, there is provided a quenched and hardened steel alloy article which has a novel combination of Y.S., CVN IE and fatigue life. In a preferred embodiment, the article comprises a transmission unit for a slurry engine. The drive unit includes a constant speed shaft and joint. The article is formed from an alloy having any of the broad, intermediate or preferred weight percentage compositions shown above. The article according to this aspect of the invention is further characterized in that it is hardened and then tempered at a temperature of 204.4°C (400°F) to 315.6°C (600°F). Alternatively, the article can be austempered to provide other Y.S. and CVN IE for applications that do not require a conventional yield strength of at least 1241 MPa (180 ksi).

[0009] According to a further aspect of the present invention there is provided a method for manufacturing a drive unit for a positive displacement drilling mud engine.

Brief description of the figures

[0010] The following detailed description will be better understood when read together with the figures, in which:

[0011] Figure 1 is a schematic of a mud engine and drill bit used in an underground drill rod train (derived from Graber, KK, Pollard, E., Jonasson, B., and Schulte, E. (Eds. ), 2002. Overview of Ocean Drilling Program Engineering Tools and Hardware. ODP Tech. Note 31. Doi:10.2973/odp.tn.31.2002).

[0012] Figure 2 is a graph of V-shaped notch impact energy for Charpy testing as a function of test temperature for the data presented in Table IV.

[0013] Figure 3 is an S-N plot of applied stress as a function of the number of cycles to fracture for the R.R. Moore rotational bending fatigue data presented in Table V.

Detailed description of the invention

The alloy according to the present invention contains at least about 0.15%, better still at least 0.18%, and preferably at least about 0.21% carbon. Carbon contributes to the strength and hardness provided by the alloy. Carbon is also beneficial to the quench strength of this alloy. Too much carbon adversely affects the toughness provided by the alloy. Therefore, carbon is restricted to no more than about 0.30% and, even better, to no more than about 0.27%. Preferably, the alloy contains no more than about 0.24% carbon for satisfactory toughness at higher strength and hardness levels.

At least about 1.7%, better still at least about 1.8%, and preferably at least about 1.95% manganese is present in this alloy primarily to deoxidize the alloy. It was found that manganese also benefits from the high strength and toughness provided by the alloy. If too much manganese is present, then an undesirable amount of austenite can result during hardening and sudden cooling such that it will adversely affect the high strength suffered by the alloy. Therefore, the alloy can contain up to about 2.3% or 2.2% manganese. Preferably, the alloy contains no more than about 2.05% manganese.

[0016] Silicon benefits from the hardenability and temper resistance of this alloy. Therefore, the alloy contains at least about 0.7% silicon, better still at least about 0.8% silicon, and preferably, at least about 0.85% silicon. Too much silicon adversely affects the hardness, strength and ductility of the alloy. In order to avoid such adverse effects, silicon is restricted to no more than about 1.1%, better still no more than about 1.0%, and preferably, no more than about 0.895% in this alloy.

[0017] The alloy according to this invention contains at least about 1.85% chromium because chromium contributes to the good hardenability, high strength and temper resistance provided by the alloy. Preferably, the alloy contains at least about 1.95% and even better at least about 2.05% chromium. More than about 2.35% chromium in the alloy adversely affects the impact toughness and ductility provided by the alloy. Preferably, chromium is restricted to no more than about 2.25% and for best results to no more than about 2.15% in this alloy.

[0018] According to this invention, nickel is beneficial to the good toughness provided by the alloy. Therefore, the alloy contains at least about 0.5% nickel, and better still, at least about 0.6% nickel. Preferably, the alloy contains at least about 0.65% nickel. The advantage provided by larger amounts of nickel adversely affects the cost of the alloy without providing a significant advantage. In order to limit the higher cost of the alloy, the alloy contains no more than about 0.9%, better still, no more than about 0.8%, and preferably no more than about 0.75% nickel.

[0019] Molybdenum is a carbide builder that is beneficial to the quench strength provided by this alloy. The presence of molybdenum increases the alloy's temper temperature such that a secondary hardening effect is achieved when the alloy is tempered from about 232.2°C (450°F) to 315.6°C (600°F). Molybdenum also contributes to the strength and impact toughness provided by the alloy. The benefits provided by molybdenum occur when the alloy contains at least about 0.1% molybdenum, better still at least about 0.15%, and preferably at least about 0.18% molybdenum. Like nickel, molybdenum does not provide an increasing advantage in properties over the significant additional cost of larger amounts of molybdenum. For this reason, the alloy contains no more than about 0.3% molybdenum, better yet, no more than about 0.25% molybdenum, and preferably no more than about 0.22% molybdenum. Tungsten can be substituted for some or all of the molybdenum in this alloy. When present, tungsten is replaced by molybdenum on a 2:1 basis.

[0020] This alloy contains at least 0.30% copper which contributes to the hardenability and impact toughness of the alloy. The alloy can contain at least about 0.4% copper and preferably contains at least about 0.45% copper. Too much copper can result in precipitation of an undesirable amount of free copper in the alloy matrix which can adversely affect the toughness of the alloy. Therefore, no more than about 0.7%, better yet, no more than about 0.6%, and preferably, no more than 0.55% of copper is present in this alloy.

[0021] Vanadium contributes to the high strength and good hardenability provided by this alloy. Vanadium is also a carbide builder and promotes the formation of carbides that help provide grain refinement in the alloy. Vanadium carbides also benefit from the quench strength and secondary hardenability of the alloy. For these reasons, the alloy preferably contains at least about 0.20% vanadium. The alloy can contain at least about 0.25% vanadium and preferably contains at least about 0.30% vanadium. Too much vanadium adversely affects the strength of the alloy because of the formation of larger amounts of carbides in the alloy which depletes the carbon from the alloy matrix material. Therefore, the alloy cannot contain more than about 0.5% vanadium and better still, not more than about 0.45% vanadium. Preferably, the alloy contains no more than about 0.40% vanadium. Niobium can be substituted for some or all of the vanadium in this alloy because like vanadium, niobium combines with carbon to form M4C3 carbides that benefit the hardenability and temper strength of the alloy. When present, niobium is replaced with vanadium on a 1.8:1 basis.

This alloy may also contain a residual amount of calcium, up to about 0.05%, which is retained from additions during alloy melting to help remove sulfur and thus benefit from the impact toughness provided by the alloy. Preferably, the alloy contains no more than about 0.02% or 0.01% calcium, and can contain as little as 0.005% calcium.

[0023] A small amount of titanium may be present at a residual level of up to about 0.05% of deoxidation additions during melting. However, the alloy preferably does not contain more than about 0.025% or more than about 0.01% titanium. Up to about 0.05% aluminum can also be present in the alloy for deoxidation additions during melting. Preferably, the alloy contains no more than about 0.025% or more than about 0.015% aluminum.

[0024] The balance of this alloy is essentially iron and the usual impurities found in commercial grades of steels and similar alloys. In this regard, the alloy may contain up to 0.025% phosphorus barb. Preferably, the alloy contains no more than about 0.01%, and even better, more than about 0.005% phosphorus. Up to about 0.025% sulfur can also be present in the alloy. Preferably, the alloy contains no more than about 0.001%, and even better, more than about 0.0005% sulfur. Cobalt is also considered an impurity in this alloy. However, the alloy can contain up to about 0.25% cobalt. Preferably, the alloy contains no more than about 0.05% or more than about 0.02 or 0.01% cobalt.

[0025] The alloy according to the present invention is balanced to provide conventional high yield strength and impact toughness in the hardened and tempered condition. In this regard, the preferred composition is balanced to provide a conventional yield point of at least about 1241 MPa (180 ksi) in combination with good toughness indicated by a V-shaped notch impact energy for fur Charpy testing. minus about 33.9 J (25 ft-lb) and less than or equal to 81.3 J (60 ft-lb) at room temperature.

[0026] Primary melting and alloy casting are preferably performed with vacuum induction melting (VIM). When desired, such as in critical applications, the alloy can be refined using Vacuum Arc Remelting (VAR). If desired, primary fusion can also be performed by arc fusion in air (ARC) or in a basic oxygen blast furnace (BOF). After melting, the alloy can be refined by electroslag remelting (ESR) or by VAR. Furthermore, the alloy can be produced using powder metallurgy techniques.

The alloy of this invention is preferably hot worked from a temperature of up to about 1149°C (2100°F) and preferably from about 982.2°C (1800°F) to form a shape. of intermediate product, in particular, elongated shapes such as billets and bars. The alloy may be heat treated by austenizing at about 862.8°C (1585°F) to about 946.1°C (1735°F), preferably at about 890°C (1635°F) to 904° C (1660°F), for about 1-2 hours. Then, the alloy is cooled in air or rapidly cooled in oil from the austenizing temperature. When desired, the alloy can be vacuum heat-treated or rapidly cooled in gas. Preferably, the alloy is tempered at about 232.2°C (450°F) to 287.8°C (550°F) for about 2-3 hours and then air cooled. The alloy can be tempered to about 315.6°C (600°F) when lower strength can be accepted.

[0028] The alloy of the present invention is useful in a wide range of applications mainly in transmission shafts and constant speed joints used in mud engines for underground drilling chains. Figure 1 shows an embodiment of a slurry motor device 10. The slurry motor device 10 includes a PCPD pump section 12. The PCPD pump section includes a rotor 14 arranged for rotation within a stator 16 in known manner . A power transmission section 18 is connected to the drill side of the PCPD pump impeller. The power transmission section includes a drive shaft 20 which is connected to one end of the PCPD pump and the other end of the drill 22. A bearing assembly 24 can be interposed around the drive shaft 20. The drive shaft 20 is connected to the PCPD pump impeller 14 to drill 22 with constant speed joints in known manner. The drive shaft 20 and constant speed joints are subjected to significant stresses when the bit encounters very hard deposits in the drilling ground. In order to withstand such stresses and resist deformation, the driveshaft and constant velocity joints are manufactured from the steel alloy described above.

[0029] The drive shaft (or drive shaft) of the slurry motor according to the present invention is formed from an intermediate product shape of the alloy, preferably bar or round rod. The intermediate form is machined to the desired diameter size and, if necessary, then ground. The machined shapes are then cut to the proper length for the drive shaft of the drive section of a mud engine. The shafts are then hardened and tempered as described above.

[0030] It is considered that the alloy of this invention may also be useful for other drilling components including flexible shafts, shock drill chucks, shock tools, and other oil well drilling tools that require a high-limit combination conventional elasticity and good impact toughness.

Operational Examples

[0031] In order to demonstrate the combination of properties provided by the alloy of this invention two 15.9 kg (35 pounds) VIM charges were cast and cast. Loads were forged into 4.03 cm2 (0.625 inch2) bars and then into standard longitudinal tensile, standard long transverse (LT) impact, standard longitudinal fatigue specimens, and standardized cubes for Rockwell hardness testing. Table I contains final chemical analyzes in percentages by weight for the two experimental loads. Table I

[0032] A heat treatment study was performed on test samples taken from Charge No. 2647. Duplicate CVN IE and duplicate tensile specimens were prepared from the alloy ingot and given the nine heat treatments (HT) shown in Table II below. The test samples were austenized in a fluid bed blast furnace for 1.5 hours at the indicated temperatures. Then, the specimens were rapidly cooled in oil from austenization temperature to room temperature, annealed for 2 hours at the indicated temperatures, and then cooled in air from annealing temperature to room temperature. The results shown in Table II include the conventional yield strength (YS) with a deviation of 0.2% and the tensile strength limit (UTS) in ksi (MPa), the elongation percentage (%El.), the percentage of reduction in area (% RA), the V-shaped notch impact energy for Charpy testing (CVN) in foot-pound (J), and the Rockwell C scale mean hardness (HRC) for each sample tested . For each heat treatment, the average properties of CVN and traction were also reported. The CVN IE test was performed in accordance with the ASTM E2312C standardized test procedure. Table II

[0033] An important consideration for any high strength steel is whether it exhibits a ductile to brittle transition temperature (DBTT). Since oil and gas drilling can be performed in geographic areas that vary widely in temperature, the alloy DBTT for the mud engine driveshaft is particularly of that application. Therefore, additional CVN samples from Charges 2647 and 2648 were tested to assess the CVN impact energy at temperatures ranging from -40.0°C (-40°F) to 65.6°C (150°F). Table III below shows the results including the load number for each test sample, the test temperature in °C (°F) (Temp.) and the CVN IE in J (pound feet) (CVN). The results are shown in graph form in Figure 2. Table III

[0034] The data presented in Table III and Figure 2 show that the alloy of this invention has essentially no ductile to brittle transition temperature over the entire temperature range tested. This means that the good toughness provided by the alloy of this invention is provided over a wide range of temperatures.

[0035] In order to demonstrate the fatigue duration provided by the alloy according to the present invention, the RR Moore rotational bending fatigue test was performed on the fatigue specimens. Prior to testing, the fatigue specimens were hardened and tempered using the C-heat treatment described above. Table IV below shows the results of the rotational bending fatigue test including the applied stress (Stress) in MPI (ksi) and the number of cycles (Cycles) until the specimen fractures. The data appear in graph form in Figure 3. Table IV

[0036] The terms and expressions used in this descriptive report are used as descriptive and not limiting terms. There is no intention in the use of such terms and expressions to exclude any equivalents of the shown and described features or portions thereof. It is recognized that various modifications are possible within the invention described and claimed herein.

Claims (19)

1. Alloy steel, characterized by the fact that it comprises, in percentage by weight, from 0.15 to 0.30 of C, from 1.7 to 2.3 of Mn, from 0.7 to 1.1 of Si, of 1.85 to 2.35 of Cr, from 0.5 to 0.9 of Ni, from 0.1 to 0.3 of Mo+1/2W, up to 0.25 of Co, from 0.3 to 0. 7 Cu, from 0.2 to 0.5 V+5/9xNb, up to 0.05 Ti, up to 0.05 Al, up to 0.05 Ca and the balance is iron and usual impurities including no more than 0.025% phosphorus and no more than 0.025% sulfur. 2. Alloy steel according to claim 1, characterized in that it contains at least 0.18% carbon. 3. Alloy steel according to claim 1, characterized in that it contains at least 1.8% of manganese. 4. Alloy steel according to claim 1, characterized in that it contains at least 0.8% of silicon. 5. Alloy steel according to claim 1, characterized in that it contains at least 1.95% of chromium. 6. Alloy steel according to claim 1, characterized in that it contains at least 0.6% nickel. 7. Alloy steel according to claim 1, characterized in that it contains at least 0.15% of Mo+1/2W. 8. Alloy steel according to claim 1, characterized in that it contains at least 0.25% of (V+(5/9xNb)). 9. Steel alloy, according to any one of claims 1 to 8, characterized in that it comprises, in percentage by weight, from 0.15 to 0.27 of C, from 1.8 to 2.2 of Mn, from 0.8 to 1.0 of Si, from 1.95 to 2.25 of Cr, from 0.6 to 0.8 of Ni, from 0.15 to 0.25 of Mo+1/2W, from 0 0.4 to 0.6 Cu, 0.25 to 0.45 V+5/9xNb. 10. Alloy steel, according to claim 9, characterized in that it contains at least 0.21 % carbon. 11. Alloy steel, according to claim 9, characterized in that it contains at least 1.95% manganese. 12. Alloy steel according to claim 9, characterized in that it contains at least 0.85% silicon. 13. Alloy steel, according to claim 9, characterized in that it contains at least 2.05% of chromium. 14. Alloy steel according to claim 9, characterized in that it contains at least 0.65% nickel. 15. Alloy steel, according to claim 9, characterized in that it contains at least 0.18% of Mo+1/2W. 16. Alloy steel according to claim 9, characterized in that it contains at least 0.25% of (V+(5/9xNb)). 17. Alloy steel, according to claim 9, characterized in that it does not contain more than 0.02% cobalt. 18. Hardened and tempered steel article, characterized in that it is formed by a steel alloy comprising, in percentage by weight, from 0.15 to 0.30 of C, from 1.7 to 2.3 of Mn, of 0.7 to 1.1 Si, 1.85 to 2.35 Cr, 0.5 to 0.9 Ni, 0.1 to 0.3 Mo+1/2W, up to 0. 25 Co, from 0.3 to 0.7 Cu, from 0.2 to 0.5 V+5/9xNb, up to 0.05 Ti, up to 0.05 Al, up to 0.05 Ca and the balance is iron and usual impurities, including no more than 0.025% phosphorus and no more than 0.025 sulfur, said article providing a conventional yield strength of at least 1241 MPa (180 ksi) and notch impact energy in V shape for Charpy test of at least 33.9 J (25 ft-lb). 19. Article according to claim 18, characterized in that it comprises a shaft for a transmission drive unit of a drilling mud engine.

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